1. Field of the Invention
This invention relates to polydiorganosiloxane elastomers reinforced with modified polyhydroxy compounds.
2. Background Information
Useful silicone elastomers are prepared by crosslinking the linear polydiorganosiloxane after incorporating a reinforcing or extending filler into the polymer. In the absence of filler, only very weak elastomers are obtained. In order to obtain the best physical properties, reinforcing filler such as fumed or precipitated silica is used. These silica fillers have very small particle size and very large surface areas, on the order of greater than 50 square meters per gram of filler. An alternate route to obtaining useful polydiorganosiloxane elastomers is the use of linear polymers obtained from copolymerizing an organosiloxane monomer together with other non-silicone monomers or to chemically graft a non-siloxane chain onto the siloxane polymer. These alternate routes are fairly complex and are not further considered.
U.S. Pat. No. 3,227,777, issued Jan. 4, 1966, shows that attempts to blend ethylene-propylene copolymers with organosiloxane and then curing the resulting composition by an organic peroxide yielded a rather poor 30 to 45 kg/cm.sup.2 tensile strength. U.S. Pat. No. 4,201,698, issued May 6, 1980, shows that when a reinforcing filler is included with such blends a tensile strength as high as 136 kg/m.sup.2 was obtained. The organopolysiloxane used had at least two functional units of either mercapto groups or aliphatic unsaturated linkages in the molecule and a specific organosilicone compound which had a polysulfide linkage and one or more silicon-bonded hydroxy groups or hydrolyzable atoms or groups in the molecule was also required to be present in the composition.
Improved mechanical properties of blends made from polyvinylalcohol (PVA) and polydiorganosiloxane are reported in Japanese applications No. 38347/78, 99987/80, and 73059/82. Improved properties are obtained when silica filler is included as a reinforcing filler.
U.S. Pat. No. 4,219,591, issued Aug. 26, 1980, claims silylated PVA compounds effective as a coating agent for inorganic silicate substrates such as glass.
Compositions of PVA, silica, and low molecular weight organic silicone compounds are taught in U.S. Pat. No. 4,567,221, issued Jan. 28, 1986, as well as in the previously mentioned Japanese applications, 38347/78, 99987/80, and 73059/82. The mixtures are suggested as defogging compounds.
Polyvinylalcohol films toughened with a plurality of microdomains dispersed throughout the polymer are taught in U.S. Pat. No. 4,608,187, issued Aug. 26, 1986.
Chemical modification of PVA with a silylating agent is known as in U.S. Pat. No. 4,617,239, issued Oct. 14, 1986. This patent discloses a silicone containing PVA agents useful in paper coatings. One method introduces a silicone moiety into a PVA by post modification with a silylating agent or addition into a derivative of PVA that contains carboxylic groups such as partially saponified polyvinyl acetate followed by saponification of the residual acetates. Another method saponifies a copolymer of vinyl ester and silicone-containing olefinic unsaturated monomer followed by addition polymerization.